Measuring under-tie support condition: An approach using distributed fiber-optic strain sensors

Previous studies have attempted to determine the under-tie support condition using strain gauges and stress cells. However, there have been limited successes due to either poor sensor accuracy or insufficient measuring points. The objective of this paper is to examine a new method using distributed fiber-optic strain sensors (DFOSSs) for predicting the tie force distribution and assessing the under-tie support condition through tie strain profile. A high-definition DFOSS was instrumented along a scale wood tie to collect strain profiles. This method includes two steps: (1) fitting the strain profiles by a customized high-order B-spline function; and (2) deriving the B-spline functions of tie bending moment, shear force, and force distribution based on Euler–Bernoulli beam theory. Test results obtained on ties with various predetermined support settings demonstrate the algorithm's ability to accurately predict support conditions. Moreover, the paper discusses the effectiveness of using shear force profiles for calculating applied loads.